The present invention relates generally to pipe connectors and, more particularly, to a connector which may be used, for example, to attach a head member or other fitting to the end of a joint of pipe, or to connect together the ends of two joints of pipe. The present invention is particularly useful in the production of petroleum products, as a means of connecting a casing head to the top of a string of surface casing in the wellhead of an oil or gas well.
In a typical completion of a conventional oil or gas well, a string of conductor pipe is driven or drilled into the earth, and a landing base is installed at the upper end of the conductor pipe. The hole for the surface casing is then drilled through the conductor pipe. The surface casing is run into the hole and cemented in place, and a casing head is installed on top of the surface casing, on the landing base. Successively smaller diameter and deeper holes are then drilled for one or more successively smaller diameter but longer intermediate casing strings, down to the oil string casing, and these casings are in turn run into the wellbore, cemented, and suspended in the wellhead. The next smaller size casing from the surface casing is typically suspended from hanger equipment in the surface casing head, and successively smaller casing strings are typically suspended from hanger equipment in separate casing spools or heads installed on top of the surface casing head. Then, after all casings are in place, a similar procedure is followed for the tubing head and tubing strings. Each time a new one of the separate heads is installed, the blowout preventer equipment, which is in place during drilling operations, is removed, leaving the hole exposed and unprotected from blowouts or other hazardous conditions until the new head is installed and the blowout preventer stack reinstalled or replaced. Thus, it is important to install the heads, including the surface casing head, as quickly as possible in order to minimize the possibility of a dangerous and potentially catastrophic blowout.
In the past, the surface casing head of an oil or gas well has generally been either threaded onto the top of the surface casing, or welded to it. Both welded and threaded connections, although simple and usually reliable, often cause difficulties requiring costly equipment repair or resulting in lost rig time, which for highly expensive rig crews and equipment can amount to a prohibitive expense. Welds can crack or otherwise fail, and usually require pre-heating, post-heating and/or stress relief, any of which operations are susceptible of being improperly performed. Welding is relatively time-consuming, and field welds may be unduly interruptive of drilling or production operations. Moreover, welding requires surface preparation beforehand and post-weld cleanup and other operations, all of which result in diminished effective drilling or production time.
Threaded connections are sometimes inadequately or improperly made up, either too loose or too tight. Cross-threading may also occur, resulting not only in an improperly made up joint, but also in thread damage in the casing head or surface casing. Threads on the head or the pipe may also be damaged in transit, storage, or handling on the rig floor. Furthermore, when a threaded connection is used, the distance the last joint of surface casing extends above the landing base is important, and must be determined with some care and proper planning. A miscalculation might result in the casing extending above the landing base a distance which is insufficient for full engagement of the connection.
One approach to avoiding these problems of welded or threaded connections has been proposed by Cameron Iron Works of Houston, Tex., with its Camforge wellhead system. In the Camforge system, after the surface casing has been installed in the wellbore and cut off above the landing base, a wellhead housing is lowered over the top of the surface casing and onto the landing base. A special hydraulic forge tool is lowered into the casing and pressured up, expanding the casing beyond yield into grooves machined in the housing and stressing the housing to near its yield strength. After the pressure is released, the housing contracts against the casing, affixing the housing to the casing and forming a metal-to-metal seal. This system, however, has its own attendant problems which detract from its desirability as a solution to the problems of welded and threaded connections. The Camforge system requires special machining in the head or housing to provide the shaped grooves into which the casing expands. The forging process which expands the casing places so much stress on the casing and housing that damage to the casing or housing can result, especially if there are any defects in the metal structure of the casing or housing. This system also requires use of a special forging tool and pump which, if either were to malfunction, might result in an inadequately made up connection or damage to the casing, housing, or rig. In addition, once installed, the wellhead housing cannot easily be removed from the casing, so the housing cannot easily be reused.
Another system which has been proposed to overcome the problems of the welded and threaded connections referred to above is the Quick Lock system of McEvoy in Houston, Tex. In that system, the casing head is lowered over the end of the surface casing until it abuts the top of the casing. Slips in the head are held in the upper or released position by one of two sets of screws. Once the casing head has landed, a second set of screws is used to lower and actuate the slips into engagement with the casing. Normally, the McEvoy Quick Lock system is used as a tieback connector where it is necessary to lower another length of pipe and connect it to the stub of an existing pipe. One major deficiency of the McEvo system is that the slips cannot be unset. Thus, once the slips are actuated, the head cannot be easily removed from the casing and reused.
There are other circumstances in addition to that of attaching a surface casing head to a surface casing string where threaded or welded connections for pipes are either inappropriate or unavailable. For example, when it is desired to attach a flange or other fitting to a pipe stub, be it part of an oil or gas production system or other piping system, it may not have a thread on or into which a threaded connection member can be installed. Welding may be impractical or impossible due to the nature of the environment surrounding the pipe stub, or the type of material of which the stub is made. In addition, in some situations it might not be possible to use alternative connection means such as the Cameron Camforge or McEvoy Quick Lock systems, such as, for example, in situations in which quick removal of the connector from the pipe is or may be necessary.
There are also circumstances which arise in which it is desired to join together the free ends of two pieces or joints of pipe, or to repair a broken pipe. As in the case of the pipe stub discussed above, welding, threading, or other means such as the Camforge or Quick Lock systems may not be available or appropriate to connect the pipe ends together.
It is an object of the present invention to provide a simple, reliable, durable, and effective pipe connection system which overcomes the problems of the prior art pipe connection devices and methods discussed above. It is also an object of the present invention to provide such a pipe connection system which is easily disconnected from the pipe or pipes to which it is attached. It is another object of the present invention to provide such a pipe connection system which may be easily reenergized in service. A further object of the present invention is to provide such a pipe connection system which utilizes leakproof metal-to-metal seals and positive gripping means.
It is an additional object of the present invention to provide a pipe connection system which requires no pre-heating, post-heating and/or stress relief, or special surface preparations or treatments of the pipe or pipes in order to effect a sealed, tight, releasable connection. Another object of the present invention is to provide such a pipe connection system which does not require specialized tools for installing and energizing the connector(s).
A further object of the present invention is to provide a connection system as described above which may be used rapidly and efficiently to securely attach a casing head to a surface casing string at a wellhead of an oil or gas well. Another object of the present invention is to provide such a connection system whereby upon cutting off the casing string below the landing base, the landing base and the casing head may be easily disconnected from the section of casing to which they are attached, and reused. A still further object of the present invention is to provide such a connection system which permits greater tolerance than with threaded connectors concerning the distance above the landing base which the top of the last joint of surface casing protrudes in order to effect a fully made up connection.
Additionally, it is an object of the present invention to provide a connection system as described above which may be used to securely and releasably attach a flange or other fitting to a pipe stub, or connect together two free ends of two joints of pipe, or repair a broken pipe.
It is a still further object of the present invention to provide such a pipe connection system which is easy to manufacture, and inexpensive.